Safety guard for abrasive wheels



Aug. 13,1935. E, LEHMANN 2,011,108

SAFETY GUARD FOR ABRASIVE WHEELS Filed May 24, 1954 INVENTOR flax Ze/zma/z/z awZze, 4,

' 7 UNITED STATES.

Patented Aug. 13, 1935 PATENT OFFICE SAFETY GUARD FOR A RASIVE WHEELS Max E. Lehmann, Park Ridge, 111., assignor to The American Laundry Machinery Company, Norwood, Ohio, a corporation of Ohio Application May 24, 1934, Serial No. 727,266 I '8 Claims. (01. 51'-268) invention relates to a safety guard for abrasive wheels and thelike, and more particularlytoa guard adapted to act as a protection against contact with the wheel after active use 1 has ceased; when the power has been shut off and the stored energy in the wheel continues its rotation.

An object of the invention is'toprovide a'safety' guard adapted to substantially completely enclose an abrasive w eel whereby to'prevent accidental 1 contact with'the wheel during the period followmanipulation-of a guard. More particularly, such a guard is arranged to close the power circuit when the guardis moved to its open position and to open or break the circuit when the guard is moved to its closed or guarding position.

'1 The invention is more fully "illustrated :and

described in the accompanying drawing and specification and the essential features are summarized in the claims. 1

In the drawing, Fig. lis aside elevation of an abrasive wheelunit, showing the safety guard in closed position;'Fig. 2 is an elevation similar to Fig. 1, showing. the. guard in open position; while Fig. 3 is a rear View of the abrasive machine, showing the safety guards in closed position and the electric circuit for operating the machine;

*It is the general practice to provide abrasive andgrinding wheels with protective guards or hoods. These hoods are often of cast construc- 1 tion and house the wheel with-the exception of y a cut-out-portion at the' point where the member tobe'ground is presented to the wheel. Such hoods protect the operator from flying particles of abrasive or metal dust or other particles-which might fly during the grinding operation. 'In such cases, the hood may be connected with an exhausting system. Another purpose of these hoods is to protect the operator from wheel explosion.

A wheel'protected as described above is. never- .theless, a source of danger after the power has been shut olT, as the wheels are often of considerable weight and travel at a high rate of speed due to the flywheel efiect. During such a period of slowing down, persons standing near the wheel 1 may come in contact therewith through an open 'portion of the hood or casingand thus receive injury; My invention provides an additional guard so connected in the power circuit which causes the rotation of the wheel as to insure that the guard will be movedto a position where it substantially encloses the entire wheel when the poweris cut'offland preferably so arranged that 5 the power circuit is closed to start the rotation 1 of the wheel when the guard is moved to its open position.-

I have illustrated my guard as applied'to a grinding machine having two abrasive wheels mounted on a common shaft; although it will be understood that the device is applicable to a singlewheel. In the apparatus illustrated, a frame It) supports a, shaft .l! for rotation by means of an electrical motor indicated generally at l2. The terminalsfor the connection of power to this motor are indicated at I3 and M. Upon the shaft H are mounted the abrasive wheels l5 and I5a. The protective devices about each of these two wheels areexactly'alike and, therefore, that connected with Wheel [5 will be described, the partsadjacent the opposite wheel being'provided with similar characters with the suflix a. 1

The customary protective hood l6, such as is often supplied to protect the operator from flying particlesor from injury due to an exploding wheel, is securely fastened to the frame it). A

cut-out portion I1 is provided to permit access to theperipheryqof the grinding wheel and a guard l9 comprising side members 20 and 2! and a peripheral member 22 so constructed as to substantially completely enclose the grinding wheel, especially the'portion normally exposed by the opening I I when the guard is in its completely closed position,,as seen in Figs. '1 and 3. This 40 guard is so mountedwith relation to the frame that it is movable into its two positions shown in'Fig's. 1 and 2, namely; the closed or guarding position of Fig. 1, and the open or out-of-guarding position of Fig. 2. The mounting illustrated comprises a bracket '23 secured to the rear side of the protective hood l6 and supporting for oscillation a, shaft 24. To the shaft is pinned a bracket 25 which is secured to the safety guard is. suitable material is secured to the top of the protective hood to act as a cushion stop for the safety guard in itsclosed position. 7 An operative connection is provided between the safety guard and the power circuit for the 55 A stop b1ock'25 of leather, fiber or other ductor bar and associated parts into contact with operating motor so as to control the opening and closing of said circuit by the moving of the guard between its two positions. The construction shown comprises an arm or finger 21 adapted to move with the guard 69 and in the form shown comprises a separate member pinned to the shaft ll.

The means for opening and closing the operating circuit of the motor in the present case comprises an electric switch 28 of known construction comprising binding posts 29 and 38 for two'sides of an electric power circuit, and having fingers 3i and 32 adapted to be connected by a conductor bar 53 which is carried by an insulating arm 35. The conductor bar and insulating arm are guided for motion into and out of com tact position by a plunger 35 reciprocably mounted in the upper portion of the switch casing and normally biased in its out-of-contact position by spring 3%. The plunger is preferably provided with a roller ti which is engageable by the arm 2'! connected with the safety guard.

It will be apparent from the apparatus described that movement of the safety guard to its open position,-as shown in Fig. 2, will cause the arm El to engage the roller 3? and move the conthe fingers (ti and 32, thus initiating operation of the motor and causing rotation of the abrasive wheel. It is also apparent that the only means for disconn cting the power circuit from the motor is to move the guard to its closed position, shown-in Fig. 1, which permits the spring 33 to move the conductor baroutwardly or to the left as seenin Fig. 1, so as to break the contact between fingers 3i and 32 and shut off the power supply to the motor. I have so arranged the parts that the power circuit is not broken until the guard is moved sufficiently toward its closed or guarding position that its center of gravity is vertically forward of the shaft 24 so that thereafter gravity will insure the continuation of the movement of the guard toward closed position if the operator should release it at that point.

Operating circuits for the motor are shown diagrammatically in Fig. 3 where LI and L2 are main supply lines, terminal M of the motor is connected by conduit 4! with L2 and the control switches indicated generally by 28 and 280, form connections in parallel between motor terminal It and Li. I

In operation, assuming that only one workman is operating the machine using wheel l5, he raises the guard 59 to the position of Fig. 2. In moving to this position arm 21 depresses plunger 35 which causes a connection between fingers 3i and 32 and completes a circuit from L! through line 3%, terminal finger 32, conductor bar 33, finger 3i, terminal 29, line 39, line Mi, motor terminalsiS, it, and line ii to L2.

When he has finished his grinding operation, lowers the guard to the position shown in Fig. 1. This opens the circuit by releasing the plunger which permits. spring 36 to disconnect the conductor bar 33 from fingers 3i and 32. In moving the guard to do this he must necessarily bring it forward pas the center of shaft I I and ther fore must allow it to come to closed position, as in Fig. 1. Thus, the wheel assembly is enclosed and there is no possibility of contact with the wheel during the coasting period following the opening the motor circuit.

If the wheel its is used instead of wheel 55, raising of the guard i911 makes a circuit to the motor from Li through line :2. terminal 38a,

finger 32a, conductor bar 33a, finger 3 I a, terminal 29a, line 43, line ll motor terminals 53, E i, and line M to L2.

If operators are working at both wheels, previously mentioned circuits are established to operate the motor. In this case, both guards are in the open position as shown in Fig. 2. When the operator at wheel its, for example, finishes his operation and closes the guard lea, the wheels will continue to operate under power until the operator on wheel 25 finishes his operation and closes the guard 59. Or, in the other case, if operator on wheel i5 finishes first and closes guard iii, the wheels will continue to be driven until the operator on 250. has finished and closed the guard ifia.

I have thus provided a guard effective to prevent injury to persons making accidental contact with an abrasive wheel coasting at high speed after power has been disconnected. This guard may well be made of light construction, for instance, of sheet metal. The arrangement of parts is such that in order to disconnect the power source from the wheel driving motor, the guard must be moved to its closed or guarding position.

What I claim is:

1. In combination, an abrasive wheel rotatably mounted upon a frame, power means for rotating said wheel, a supply circuit for said power means, a control member for opening and closing said circuit, a guard mounted on said frame for movement into and out of guarding position, said guard in guarding position being adapted to substantially enclose said wheel, and operative connections between said guard and control member for causing movement of said member to circuit closing position when said guard moves out of guarding position and for causing movement of said member to circuit opening position when said guard moves into guarding position.

2. In combination, an abrasive wheel rotatably mounted upon a frame, electric motor means for rotating said wheel, an electric power circuit for operating said motor, a switch in said circuit, a guard adapted to enclose said wheel and movable to open and closed positions, an arm movable with said guard, and said arm being constructed and arranged to cause closing of said switch when said guard is moved to open position and to cause opening of said switch when said guard is moved to closed position.

3. In combination, two abrasive wheels rigidly mounted upon a shaft, power means for rotating said shaft, a supply circuit for said power means, two control members arranged in parallel for opening and closing said circuit, a guard for each wheel movable to open and closed position, each guard in closed position being adapted to enclose its wheel, each guard having an operative connection with one of said control members constructed and arranged to cause movement of the said control member to circuit closing position when the guard is movedto open position.

i. In combination, an abrasive wheel rotatably mounted upon a frame, means for rotating said wheel, a safety guard mounted on said frame for movement into and out of guarding position, said guard being constructed and arranged substantially to completely enclose said wheel when in guarding position, and means rendering said wheel rotating means operative only upon movement of the guard out of guarding position.

5. In combination, an abrasive wheel rotatably V mounted upon a frame, means for rotating said I g 2,011,108 wheel, a safety guard mountedon said frame for movement intoand out ofguarding position, said guard being constructed and arranged substantially to completely enclose said wheel when in guarding position, and means rendering said wheel rotating means inoperative upon move ment of the guard into guarding position.

6. In combination, an abrasive wheel rotatably mounted upon a frame, means for rotating said 7 constructed and arranged to move automatically to completely closed position after movement by an operator to a partially closed position, and

means rendering said wheel rotating means inoperative upon movement of said guard to said partially closed position.

7. In combination, an abrasive wheel rotatably mounted in a frame, electric motor means for rotating said wheel, an electric power circuit for operating said motor, a control switch for said circuit, an operator-operated guard adapted to enclose said wheel and pivotally mounted on a shaft to the rear of said wheel, said guard being movable about said shaft to open and closed positions, an arm rigid with said shaft, and said arm and switch being so arranged that said arm closes said switch when said guardis'moved to open position.

8. The combination of claim '7, in whichsaid guard and arm and switch are so arranged that said arm opens said switch only when said guard has been moved to such position that gravity will complete its closing movement when the operator releases said guard. a i 

